ME1008: MANUFACTURING TECHNOLOGY

UNIT ICASTING

INTRODUCTION TO CASTING

Casting is a manufacturing process by which a

liquid material is usually poured into a mold,

which contains a hollow cavity of the desired

shape, and then allowed to solidify.

It is most ancient process of manufacturing

metallic components.

INTRODUCTION TO CASTING

Following steps involved in the casting processMelting the metal.Pouring it into a previously made mould or cavity.Cavity which conforms the shape of the desired

component which we obtained.Allowing the molted metal to cool and solidify in the

mould.Removing the solidified component from the mould.Cleaning it for further treatment if necessary.Note: “the solidified piece of metal which is taken out of mould

is casting”

APPLICATIONSAPPLICATIONS

Engine and cylinder block.

Pistons, piston rings

Wheels and housing of steam and hydraulic

turbines.

Turbine and jet engine blades, etc.

CLASSIFICATION OF CASTING PROCESS

Expandable mould casting, one casting mould with

less accuracy, eg: sand casting.

Permanent mould casting, mould will used repeatedly

for number of casting be achieved, it is used for mass

production and it with high accuracey.

Semi-permanent casting, high refractory materials is

used, so it is not suitable for permanent moulding.

PATTERNS

In casting, a pattern is a replica of the object to be

cast, used to prepare the cavity into which molten

material will be poured during the casting process.

It is not exact replica of the exact desired casting.

It is slightly larger than the desired casting, because

of allowances.

TYPES OF PATTERN

Single piece pattern

Split piece pattern

Loose piece, Gated, match pattern

Sweep pattern

Cope and drag pattern

Skeleton pattern

Shell and follow board pattern.

TYPES OF PATTERN contd….Single piece pattern: It is simplest of all pattern

is made in one piece. It is suited for limited process only.

Spilt piece pattern: It is used for intricate casting for usual shapes. These two patterns are joined together with the help of dowel pins.

TYPES OF PATTERN contd….

Loose piece pattern: Some patterns usually

single piece are made to have loose pieces in

order to enable their easy with drawn from the

mould.

TYPES OF PATTERN contd….

Gate pattern

Match plate pattern

TYPES OF PATTERN contd….

Cope and drag

Sweep pattern

TYPES OF PATTERN contd….

Skeleton pattern

Followpattern

TYPES OF PATTERN contd….

Shell pattern

REQUIREMENTS OF A GOOD PATTERN

Secure the desired shape and size of the casting.Cheap and readily repairable.Simple in design for ease of manufacture.Light in mass and convenient to handle.Have high strength and long life in order to

make as many moulds as required.Retain its dimensions and rigidity during the

definite service life.Its surface should be smooth and wear resistant.Able to withstand rough handling.

DESIGN CONSIDERATION IN DESIGN CONSIDERATION IN PATTERNSPATTERNS

1. Proper allowance should be provided.

2. The parting line should be carefully selected.

3. Proper material should always be selected.

4. The wall thickness and sections should kept as

uniform as possible. Abrupt changes should invariably

be avoided.

5. The use of offset pairing, instead of cores, should be

encouraged to as great extent as it is possible. Abrupt

changes should invariably be avoided.   

PATTERN LAYOUT

Pattern making consists of two different stages to prepare a layout and to shape the different parts. Layout consists of the following steps:a. Initially study the drawing pattern and select a wood that can suitably accommodate two views.b. Take on surface of the wood as base and plane the adjacent surface.c. Take a folding rule and measure the dimensions as per the drawing.d. Prepare the layout by using various measuring and marking tools locating position of core prints and surface to be machined.

PATTERN MATERIALS

Wood: Piece and short run production

Metal: Large scale and mass production

Cement, Plastics for example epoxy resin: Batch

production.

ALLOWANCEALLOWANCE

Shrinkage allowance

Machining allowance

Pattern draft or tapper

Corners and fillets

Rapping or shake allowance

Distortion allowance

MOULDING SAND

Molding sand is also known as foundry sand.

Sand with moistened and compressed to pack well

and hold its shape.

It is used in the process of sand casting.

Green sand is an aggregate of sand, bentonite clay,

pulverized coal and water.

Main purpose of this sand to make mould cavity for

casting process.

MOULDING SAND contd… Green sand:

It is sand used in the wet condition for making the mould. It is

mixture of silica sand with 15-25 per cent clay and 6-8 per cent

water

Green sand moulds are not dried and metal is poured in them in

the wet condition

Being damp the sand can be easily worked with hand to give it

any desired shape

This sand is used for producing small to medium sized moulds

which are not very complex

MOULDING SAND contd…

Loam sanding:

Loam sand is sand containing up to 50 % clay

which has been worked to the consistency of

builder mortar.

This sand is used for loam sand moulds for

making very heavy castings usually with the

help of sweeps and skeleton patterns.

MOULDING SAND contd…

Dry sand:If we dry the green sand mentioned above, then we get dry sand. the physical composition remains same, except for water content.

Facing sand:This sand comes in contact with direct contact of molten metal hence it is subjected to severest conditions. the basic composition is silica sand and clay.

GATING AND RISERING

The assembly of channels which facilitates the molten metal to enter into the mold cavity is called the gating system.

Gating also called as sprue.

Goals of Gating System:

The goals for the gating system are: To minimize turbulence to avoid trapping gasses into the mold To get enough metal into the mold cavity before the metal starts

to solidify To avoid shrinkage Establish the best possible temperature gradient in the

solidifying casting so that the shrinkage if occurs must be in the gating system not in the required cast part.

Incorporates a system for trapping the non-metallic inclusions

CORECORE

A core is a device used in casting and molding

processes to produce internal cavities and

reentrant angles.

The core is normally a disposable item that is

destroyed to get it out of the piece.

They are most commonly used in sand casting,

and also used in injection molding method.

SHELL MOULD CASTING

• Shell mold casting is a metal casting process

similar to sand casting.

• Molten metal is poured in mold cavity.

• In shell mold casting, the mold is a thin-

walled shell created from applying a sand-

resin mixture around a pattern.

SHELL MOULD CASTING contd….

Metal piece pattern is used, so it reused to make

more number of mould.

It allows the higher production rate.

Shell mold casting allows the use of both

ferrous and non-ferrous metals, most commonly

cast iron, carbon steel, alloy steel, stainless steel,

aluminum alloys, and copper alloys used.

SHELL MOULD CASTING contd….

The shell mold casting process consists of the following steps:

Pattern creation: A two-piece metal pattern is created in the shape of the desired part, typically from iron or steel.

Other materials such as aluminum for low volume production or graphite for casting reactive materials.

SHELL MOULD CASTING contd….

Mold creation - First pattern is heated to 175-370°C (350-700°F) and coated with a lubricant to facilitate removal.

Next, the heated pattern is clamped to a dump box contains a mixture of sand and a resin binder.

The dump box is inverted, allowing this sand-resin mixture to coat the pattern.

The heated pattern partially cures the mixture, which now forms a shell around the pattern.

Each pattern half and surrounding shell is cured to completion in an oven and then the shell is ejected from the pattern.

SHELL MOULD CASTING contd….

Mold assembly - The two shell halves are joined

together and securely clamped to form the

complete shell mold.

If any cores are required they are inserted prior

to closing the mold. The shell mold is then

placed into a flask and supported by a backing

material.

SHELL MOULD CASTING contd….

Pouring - The mold is securely clamped

together while the molten metal is poured from a

ladle into the gating system and fills the mold

cavity.

Cooling - After the mold has been filled, the

molten metal is allowed to cool and solidify into

the shape of the final casting.

SHELL MOULD CASTING contd….

Casting removal - After the molten metal has

cooled, the mold can be broken and the casting

removed.

Trimming and cleaning processes are required to

remove any excess metal and sand from the feed

system.

INVESTMENT CASTING

Investment casting is an industrial process based

on and also called lost-wax casting.

The first step in investment casting is to

manufacture the wax pattern for the process. 

INVESTMENT CASTING contd….

INVESTMENT CASTING contd….

INVESTMENT CASTING contd….

INVESTMENT CASTING contd….

INVESTMENT CASTING contd….

INVESTMENT CASTING contd….

CENTRIFUGAL CASTING

CENTRIFUGAL CASTING In this process molten metal is poured into a spinning die.

The die can be spinning either on a vertical or horizontal

axis depending on the configuration of the desired part.

Ring and cylinder types cast vertical centrifugal process.

Tubular shapes are made with the horizontal centrifugal

process.

CENTRIFUGAL CASTING contd….

Permanent mold is rotated continuously about

its axis at high speeds (300 to 3000 rpm) as the

molten metal is poured.

The molten metal is centrifugally thrown

towards the inside mold wall, where it solidifies

after cooling. 

CENTRIFUGAL CASTING contd….

Castings can be made in almost any length, thickness and diameter.

Different wall thicknesses can be produced from the same size mold.

Eliminates the need for cores.Resistant to atmospheric corrosion, a typical

situation with pipes.Mechanical properties of centrifugal castings are

excellent.Only cylindrical shapes can be produced with this

process.

CENTRIFUGAL CASTING contd….

Features of centrifugal casting: Castings can be made in almost any length, thickness

and diameter. Different wall thicknesses can be produced from the

same size mold. Eliminates the need for cores. Resistant to atmospheric corrosion, a typical situation

with pipes. Mechanical properties of centrifugal castings are

excellent. Only cylindrical shapes can be produced with this

process.

DEFECTS IN CASTING

Open Blows and Blow HolesPin Hole PorosityEntrapped Air and other gasesCracked CastingBent or Twisted CastingDropped MouldFusionSwellRun outMismatchMis-run and Cold Shut